My husband and I are both very nearsighted. For our upcoming cruise, I was looking to get him a a "prescription mask" too. (I have a -5) If you just want nearsighted correction, I found a couple for around $50 on that major online retail website but that was still more than we wanted to spend for something we do not need that often. I found swim goggles (not a mask) with correction for under $20 but I know those are dangerous for diving below the surface. I then checked ebay and found a source in China that had some for under $20. The lead time was longer than we are used to but they did arrive well within the promised time The correction seems good. The mask is much light weight than mine and the strap a lot thinner. We need to see how the fit is next time we get in the hot tub. Unlike some other offers, they did say you could order different correction for each eye.
I would not suggest them for scuba or for someone who plans to use frequently, but for a little snorkeling they should do the trick.